1. Field of the Invention
The present invention relates to a device for optical interconnection between component cards placed within the case of an electronic equipment unit.
2. Description of the Prior Art
It is a conventional practice to construct an electronic equipment unit in which electronic components are mounted on cards and connected to each other by means of pointed circuit tracks. When a number of cards are employed, the cards are usually placed side-by-side and plugged into metal cases or so-called "packages" with their faces parallel to each other. The bottom wall of the package is provided with an array of multicontact electric connectors to which the cards are connected, said connectors being in turn joined to each other by means of a system of connecting leads. The cards are then guided and maintained by means of rails fixed on package walls and are intended to be plugged into the multicontact electric connectors. It is possible in some instances to establish connections between the connectors by means of a parent board formed with a printed circuit but it is often necessary to establish wire connections by reason of their number and their densely intercalated relationship. These card-edge connectors are not always sufficient and it often proves necessary to make use of complementary connectors on the front face of the package and sometimes even on the card faces. In such instances, the complementary connectors are coupled by means of conductors assembled together in the form of cables in order to facilitate extraction of cards. It is therefore wholly desirable to limit as far as possible the number of connecting leads which pass through the different connectors. This is even more true in the case of high-delivery connections which call for special precautions, such as coaxial cable connections which are very difficult to use in such an environment.
Particularly in the case of high-delivery connectors, it has consequently been proposed to make use of additional connections by optical means, or so-called optical links.
In the prior art, two main approaches have been adopted for establishing connections in the form of optical links.
In a first approach, an optical fiber is employed as a connecting lead between two cards. One end of the fiber is optically coupled to a light-emitting source which is modulated by data to be transmitted. The other end of the optical fiber is coupled to a light detector for converting light to electric signals. The source and the detector are naturally mounted on two different cards between which the optical link is to be established.
Provision must accordingly be made for transmitter and receiver bases, for connectors or similar elements and devices adapted to implantation on a printed circuit card.
An arrangement of this type is described, for example, in French patent Application No. FR-A-2,437,057.
This arrangement fails to overcome the disadvantages mentioned, that is to say the large number of physical connection layers or cables on the front or rear faces of the cards.
In another approach, it has been proposed to establish direct optical links between adjacent cards.
A communication is thus established by means of a light-emitting source placed on a first card and by means of a light detector fitted with a collimating lens and placed opposite to said light source on an adjacent second card.
This arrangement is described in French Certificate of Utility No. FR-A-2,537,825.
However, the optical links can be established only between two adjacent cards and not between two cards placed at any location in the package. Furthermore, it is necessary to provide each light detector with an additional discrete element consisting of a collimating lens.